In order to describe the scope of the current invention it is desirable to briefly outline the operational procedures of facsimile communications and the incorporation of file transfer within these procedures. This may be done with reference to the five Phases in a facsimile transmission:
Phase A is the call establishment and line connection of equipment,
Phase B is the pre-message signalling and capability selection,
Phase C is the facsimile message transfer,
Phase D is the post-message signalling, and
Phase E is the call disconnection.
In particular Phase B is the low speed (300 baud) pre-message signalling in which the capabilities of the respective machines are indicated and selected. In particular the called station first responds with a Digital Information Signal (DIS) in which its capabilities in terms of group type, speed, resolution, and other special capabilities are indicated. At this time file transfer capabilities may also be indicated. The calling machine then responds with a Digital Command Signal (DCS) in which, in line with its own capabilities, the capabilities required for the forthcoming transmission are selected. This is followed by a high speed training sequence related to synchronisation, equalisation and other functions.
When the receiving machine indicates its readiness to receive, Phase C is entered during which the transfer of facsimile information takes place. At this time the transmitting machine will progressively scan the input document, code and compress the pixel information according to the selected resolution and transmit the information at the selected speed. The receiving machine will correspondingly decompress and decode the received information and print the required image.
At the completion of each page, Phase D is entered. This post-message signalling determines if there are more pages to transmit, in which case Phase C is repeated. If there are no more pages then Phase E is entered at which time the call is terminated and the line disconnected.
It is necessary to refer to recent modifications to the standards for facsimile telecommunications as determined by the Study Group VIII of the CCITT. These allow for improvements in speed, resolution, network addressing procedures and also for file transfer to be accomplished as an alternative facsimile data type.
The procedures for non-facsimile image data transfer within the facsimile call are defined in modifications and appendices to the CCITT Recommendations T.4 and T.30 which govern facsimile telecommunications. In particular the file transfer modes permitted are:
(a) Basic Transfer Mode (BTM), PA0 (b) Document Transfer Mode (DTM), PA0 (c) Binary File Transfer (BFT), and PA0 (d) Edifact transfer. PA0 i) a first termination means for direct connection of a facsimile transceiver, PA0 ii) a second termination means for direct connection of a computer, PA0 iii) first communication means for communicating with the facsimile transceiver via said first termination means, PA0 iv) second communication means for communication with the computer via said second termination means, and PA0 v) control means for controlling the first communication means and the second communication means,
Of these, BFT is considered most general and most suitable for widespread application for PC compatible communications. This is because the binary file mode allows the transfer of any type of file including those indicated by the other modes. The first two transfer modes are more appropriate for integration with telex or similar communications, whereas the fourth relates specifically to the standard form for electronic data interchange for administration commerce and transport (EDIFACT).
Whereas for the following description of the preferred embodiments of the present invention, the binary file transfer mode will be most relevant, the preferred embodiments may include equipment which is capable of transceiving file information in any of the above modes and interfacing with equipment which is designed specifically for the transception of information in any of the above file transfer modes.
File transfers may be affected, with a compatible receiver, by making the appropriate DCS selection in Phase B. This may be after the completion of a normal facsimile transfer in Phase C. In this case, Error Correction Mode (ECM) will also be selected to guarantee data integrity. File transfer will take place in Phase C according to the BFT or other selected file transfer mode.
In the case of a facsimile device for a personal computer, the file or files selected for transfer, and those received will normally reside on the hard disk or floppy disk of the personal computer, according to the user's specification. In the case of non-computer based devices, the files for transception will normally reside on a floppy disk.
With all facsimile devices the facility may exist for the calling device to receive facsimile information from a remote called device which has a document to transmit (polling). This facility is also relevant for file transfers, as per CCITT Recommendation T.30.